From WO 2007/008930 A2, a method of monitoring a range of motion of a body part is known, wherein a housing including a sensor is positioned against said body part, and wherein, in a first measuring step, a first orientation of an apparent gravity force acting on said housing is obtained while said body part has a first orientation relative to adjoin to which said body part is coupled and, in a second measuring step, a second direction of the apparent gravity force acting on said housing is obtained, while said body part has a second orientation relative to the joint. In a determining step, a magnitude of rotation of said body part from the first orientation to the second orientation is determined based upon the first and second directions of said apparent gravity force.